Prosecutors allege that Yang poisoned his roommate, Juwan Royal, with thallium and other chemicals by lacing his food and drinks.

Thallium is odourless and tasteless soft metal and can be fatal in humans. It used to be used in rat poison but was banned for that use in the 1970s.

Mr Royal sought medical help several times because he felt dizzy and was throwing up. He later tested positive for thallium. He experienced extreme pain in his lower extremities as well as severe burning and numbness.

Yang said that he bought thallium and other chemicals on the internet but was going to use them to harm himself if he did not do well on future exams.